Cable television networks are no longer purely distribution networks used for TV and radio distribution, but now also provide access for the customer to the networks. Thus TV and radio signals are distributed from a local centre or optical node by way of a signal splitter with an output connected to each customer. Return traffic from each customer is returned through the splitter to the local centre or optical node and thence to the rest of the network. Such return traffic might include requests for pay-per-view television programmes.
Usually the traffic from the customer to the local centre or optical node is called “return path traffic” or “upstream signals”. The upstream signals are transported using a different frequency range than the distribution signals (usually called “downstream signals”) originating from the network provider. Modern cable TV networks typically use 5 MHz to 65 MHz for upstream signals and 85 MHz to 862 MHz for downstream signals, although other frequency ranges are also used.
All upstream signals, no matter how they originate, are transported to the local centre or optical node. Thus unwanted noise in upstream signals will also be injected into the network. The unwanted signals originate from various sources but a major part is due to radiation of outside transmitters in the used upstream frequency range. The total sum of these unwanted signals is known as “ingress”. The majority of ingress originates from the in-house installation of the customer and is therefore injected into the network at a customer access point. This ingress is a major problem in the network since all these unwanted signals are summed and will limit the signal to noise ratio (and therefore the capacity) of the upstream signals.
It is an aim of the present invention to provide a signal splitter circuit which reduces noise ingress into a cable television distribution network.